Check data in firebase database

Ionic Framework ionic-v3
1

I have app containing register and login page
this register.is

import { Component } from '@angular/core';
import { NavController ,ToastController,AlertController ,LoadingController } from 'ionic-angular';
import { FirebaseService } from '../../services/firebase.service';
import { Validators, FormBuilder, FormGroup, FormControl } from '@angular/forms';
import { Observable } from 'rxjs/Observable';
import { map } from 'rxjs/operators';
import { LoginPage } from '../login/login';

@Component({
  selector: 'page-home',
  templateUrl: 'home.html'
})
export class HomePage {
  home:HomePage;
  simple_form: FormGroup;
  constructor(public navCtrl: NavController ,  public loadingCtrl: LoadingController,
    public alertCtrl: AlertController,public firebaseService: FirebaseService, public toastCtrl: ToastController,public formBuilder: FormBuilder) {
      this.simple_form = this.formBuilder.group({
        name: ['', Validators.required],
        email: ['', Validators.required],
        pass: ['', Validators.required],
      });
  }

async createSong() {
  const loading = await this.loadingCtrl.create();

  const name = this.simple_form.value.name;
  const email = this.simple_form.value.email;
  const pass = this.simple_form.value.pass;


  this.firebaseService
    .createSong(name, email, pass)
    .then(
      () => {
        
          let toast = this.toastCtrl.create({
            message: 'User was created successfully',
            duration: 3000
          });
          toast.present();
      
      },
      error => {
        console.error(error);
      }
    );

  return await loading.present();
}

loginpage(){
  this.navCtrl.push(LoginPage);
}

}

this rgister.html

<ion-content padding>
    <form [formGroup]="simple_form"  (submit)="createSong()" >
        <ion-item>
          <ion-label floating >Name</ion-label>
          <ion-input type="text" formControlName="name" class="form-controll" required></ion-input>
        </ion-item>
  
        <ion-item>
          <ion-label floating >email</ion-label>
          <ion-input type="email" formControlName="email" class="form-controll" required ></ion-input>
        </ion-item>
  
        <ion-item>
          <ion-label floating >password</ion-label>
          <ion-textarea type="password" formControlName="pass" class="form-controll" required ></ion-textarea>
        </ion-item>

        <button ion-button full [disabled]="!simple_form.valid " type="submit">Add</button>

      </form>

      <button ion-button full  (click)="loginpage()" >login</button>

  </ion-content>

this login.html

<ion-header>

  <ion-navbar>
    <ion-title>Login</ion-title>
  </ion-navbar>

</ion-header>

 <ion-content padding>
 	<form  [formGroup]="loginForm" (ngSubmit)="login()">

        
    <ion-item>
      <ion-label floating >email</ion-label>
      <ion-input type="email" formControlName="email" class="form-controll" required ></ion-input>
    </ion-item>

    <ion-item>
      <ion-label floating >password</ion-label>
      <ion-textarea type="password" formControlName="pass" class="form-controll" required ></ion-textarea>
    </ion-item>
  <button ion-button full  type="submit" (click)="goback()" >login</button>
      </form>

  </ion-content>

in the login page, I want to check if email and password exist in the database if exist and correct, let user login to the app.
how do that, please help me